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6 Methods to create the plan 171

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Critical Chain Project Management

the completion time (start time plus duration) on the lower right
corner.

8. Calculate the feeding paths using a backward pass from where
they enter the critical chain.
9. Remove any remaining resource contention and revise the calculation.
10. Identify the locations for the resource buffers.
11. Size the resource buffers.
This process is not difficult for projects with 10 to 50 tasks. It gets
harder after that.
You may refine the method by cutting out colored paper bars to
represent each task. The length of the bar represents task length, and the
bar color represents the task duration controlling resource. That simplifies
the resource contention steps and subsequent calculation. It obviously
requires a little more upfront preparation. Large projects have used this
method successfully with over 500 tasks. Using a magnetic scheduling
board is another way to implement the same idea.
6.6.2

Critical path software

You can use critical path software to plan and manage critical chain
projects. Most software packages have sufficient options to support you
in leveling the resources and using late start on the feeding chains. You
always start from the same place: with a project logic containing the
reduced task times and resource requirements. You should ensure (when
necessary) that you have selected the appropriate options to maintain the
fixed task duration that you input and that you have selected options to
late-start each path. Sometimes, you can do that globally. Other times,
you can put constraints on the first task on each path that causes all the
downstream tasks to late-start. (You need to experiment and understand
what your software does to those options or constraints during resource
leveling.)
Most critical path software provides options for the algorithm to
perform resource leveling. You can experiment with them. The critical

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chain method does not depend on the algorithm you use. It simply
requires that the final plan have removed all resource contention within
the single project. Usually, you can do resource leveling manually and
view the final resource allocations by task.
After initially leveling resources, you must identify the critical chain.
We suggest you add links to the plan to cause the resource leveling to stay
in place. You can then remove other constraints that your software may
have added to implement resource leveling (e.g., some software adds
fixed task start-date constraints to implement resource leveling). If you
do add logic connections, you then should be able to calculate the schedule and have the critical path equal the critical chain.
Make sure the critical chain you identify really is the constraint of
your project. Sometimes an inadvertent logic connection results in tasks
on the critical chain that cannot or should not determine the duration
of your project. (We call such a connection a mathematical critical
path/chain.) Adjust logic or task duration to cause the critical chain to be a
legitimate constraint to your project. (Note again that there may be two
nearly equal length paths vying for the critical chain. We suggest you
choose the one that you feel has higher uncertainty or that makes most
use of a potentially capacity-constrained resource.)
The distribution of tasks on the critical chain must provide effective
immunity from variation in any one task. There are two simple guidelines
for doing that.

1. Make sure the critical chain comprises at least 10 tasks (unless
your project is very small).
2. Make sure no single critical chain task comprises more than about
20% of your critical chain or more than 50% of your project
buffer.
Next, add the feeding buffers and the project buffer. You add these as
tasks, without resource requirements. Remember to tie in the feeding
buffers as predecessors to the critical chain task at the point they join the
critical chain. Then recheck the resource leveling and make any final
adjustments. (Adding the feeding buffers usually requires redoing some
amount of resource leveling.)

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6.6.3

Critical Chain Project Management

Critical chain software

Critical chain software automates most or all of the process. Several
software packages are currently available, and we understand that most
major project management software will be adding the capability over
the next year. The most widely available software currently used is
ProChain, an add-on to Microsoft Project. Concerto is another currently available product.

6.7

External constraints

Projects may have external constraints, which can influence the project
lead time and which are not under the control of the project team. Regulations, inspections, and permits often fall into this category. External
constraints may be internal to the company, such as another division that
has to provide an essential component.
The five focusing steps provide a method to deal with external constraints. First, you must identify them as constraints (or as potential
constraints) and deal with them accordingly. If they are only potential constraints, you can deal with them under project risk management.
If you feel that the likelihood for a potential constraint becoming an
actual constraint is large, you may want to make sure that it is on the
critical chain.
The second step is to exploit the constraint. In the case of regulations
and permits, that usually requires providing a high assurance that all
submissions to the regulators meet their needs completely. That may
require additional resources upfront. You should consider, however, that
any delay in the project critical chain should be valued for the burn rate of
the entire project or the expected daily return upon completion of the
project. You may elect to hire experts in the particular area to help ensure
success. There may be portions of the project that can be exempted from
the constraint.
The third focusing step subordinates everything else to the constraint.
That may require doing additional scope or investing additional management time to ensure good working relationships to any people or agencies
that may become an external constraint, as it is not usually under your
control.
It is improbable you would elect to elevate an external constraint.

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6.8 Reducing planned time (a.k.a. dictated
end dates)
Project managers are often asked to accelerate schedules. With CCPM,
there may be a tendency to look at the juicy project buffer and suggest
that reducing the buffer is a painless way of reducing the planned project
lead time. Reducing the project buffer has no impact on project execution
time; it only reduces the chances that you will meet your promised
lead time and causes excessive buffer triggers. Excessive buffer triggers
damage project performance. Therefore, do not cut the project buffer.

6.8.1 Acceleration without cost impact (exploit and
subordinate to the constraint)

Several sensible methods can reduce project lead time. Preferred options
do not increase cost. Two primary options are to get additional resources
when resolving contentions caused the lead time to be increased and to
look inside the tasks for batching opportunities.
You may need only a short time of an additional resource to make
a significant improvement in the project overall lead time. If there is a
way to obtain the additional resource, this method can reduce the overall
project lead time at no additional cost, since you had to perform the tasks
for the same individual durations, that is, you do not change the task
work (person-days). You can reduce the project buffer if such a change
reduces the length of the critical chain.
Batching occurs when a task includes more than one physical output.
For example, a task may include making a number of certain parts used in
the final assembly. The parts may be identical or different and are not
limited to hardware. They might include different technical products,
such as drawings, parts lists, or reports, or even different people, such as
hiring people to staff one shift at a time.
The successor task may be able to start when the first of the predecessor outputs is available. In that case, you can break up the task into
smaller pieces to better show the real workflow. Your plan can also show
that type of relationship as a task start-to-start dependence, with a lag.
Alternatively, you can show it as a finish-to-finish task logic. Whichever
way you choose, your management process should ensure that performers understand and focus Roadrunner performance (i.e., start the task as

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soon as input is available, focus on it 100% until done and pass on your
result) on each individual task output. They must keep the sequence
needed to realize the assumptions made in your plan.
If batching involves a significant number of parts, you may want to
invoke a supplemental method to track and control the parts through the
repetitive process. The critical chain plan would show the process as a
single activity, for example, “Process 37 parts.” One effective method uses
the line-of-balance method, combining features of operational process
control with project management. The line-of-balance method plans the
time for each part to traverse the process flow, creating an expected
number of parts through each step at a given time (the line of balance).
Tracking compares the actual parts through each process step to the line
of balance.
6.8.2 Acceleration with increased raw material cost
(elevate the constraint)

You can also reduce project time by exercising higher-cost alternatives. For example, you can use overtime or hire additional temporary
resources (which usually cost more). You may be able to purchase
components with a higher cost but a shorter lead time. You may be able to
use higher premiums for early subcontract delivery.
TOC suggests that considerations of increased cost compare the additional operating expense to the impact on project throughput. The
throughput of project acceleration (per day) is the value of the whole
project (per day). Compare the cost of increased raw material cost to the
throughput increase from the acceleration. If the throughput increase
exceeds the cost increase, you should elevate the constraint.

6.9

Enterprisewide resource planning

You can use enterprisewide scheduling tools to identify to the resource
managers the anticipated window and duration of tasks they have to
support. Resource managers must buy in to understand that the dates
are not meaningful; we focus on windows of performance and task
duration estimates. The resource managers can then assess if their longterm aggregate demand requires more or fewer resources and allocate
resources based on the criteria.

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6.10

177

Frequently asked questions

Sometimes, abnormal things seem to happen, and questions arise. This
section addresses those situations and questions.
◗ After we add the feeding buffers, noncritical chains start earlier than the

critical chain. Why?
That can happen and should not be a cause for concern. Start the
project with the noncritical chain. Be sure to use a resource buffer
on the first task on the critical chain. An alternative method relocates the excess feeding buffer (i.e., that which pushes the feeding
path before the critical chain) just ahead of the project buffer.
◗ When we add the feeding buffer to a noncritical chain with a critical chain

task as a logical predecessor, it pushes the critical chain task back, creating a
gap in the critical chain.
If the change required is a small percentage of the project buffer,
make the critical chain feeding buffer a little smaller than the buffer
sizing indicates. For other cases, consider where the noncritical
chain feeds the critical chain and the relative variability of the
two chains. You may also relocate the excess feeding buffer to
just before the project buffer. Remember, we are subordinating
everything else to the critical chain. In general, gaps in the critical chain should happen only because of a company constraint
resource. Gaps in the plan do not mean you should have a gap in
performance.
◗ Why do we not connect the other chains by their resource and path

dependencies?
It is not necessary, and attempts to add that level of detail do not
improve project performance. Fluctuations will occur, so attempting to control every dependent chain is not possible. The CCFBs and
the use of buffer management provide the necessary and sufficient
control.
◗ Our schedules have thousands of tasks, so there is no way to plan the project

without an effective computer program.
Question your assumptions. Is it logical to assume that increasingly
detailed complexity in a project plan will make the project more